AIDS has emerged as a significant pediatric disease with the rate of infection in neonates born to HIV-infected mothers reported to be from 20-50%. Although the clinical course in pediatric patients is variable, it is known to be more rapidly fatal when compared to adults. Identification of new pediatric therapies is clearly warranted due to the rapidity and severity of disease, although safety and efficacy must be proven. These issues are further intensified when considering treatment of gravid patients since fetal exposure can occur, which may result in long-term, unexpected effects. A preliminary study was performed in order to assess the safety and placental transfer of a new antiretroviral agent, (R)-9-(2-phosphonylmethoxypropyl)adenine (PMPA), when administered subcutaneously to the dam during the second and third trimesters (30 mg/kg once daily). The fetus was sonographically monitored weekly during gestation to assess growth and development, and blood samples were collected roughly 30 minutes post-treatment from the fetus and dam approximately every 10 days during the treatment period. Fetal and maternal blood samples were assessed for PMPA concentration and subjected to hematologic evaluation. Results indicated no adverse effects in the fetus or dam during the course of treatment, with delivery of a normally-grown infant at term. Placental transfer of PMPA was significant at all prenatal time points studied. A mean (1SD) fetal serum concentration of 9.613.4 mg/ml and mean maternal serum concentration of 57.218.8 mg/ml was detected; the mean maternal:fetal ratio of PMPA was determined to be 17.016.5%. Further studies which focus on the safety and efficacy of PMPA when administered to the gravid monkey during the course of gestation are currently in progress. *KEY*Fetus, Hematopoiesis, Growth, Placental transfer, PMPA, Toxicity